A content addressable or associative memory is a data storage facility that permits a data processing system to rapidly determine whether a particular piece of information is stored in that facility by performing a simultaneous examination of the entire contents of the memory, rather than by successively scanning through all the addresses and examining the contents of each addressed location on an individual basis. Because each memory device within a conventional content addressable memory contains only one storage entry per bit line, which memory devices are to affect the results of an associative read operation cannot be individually controlled. Instead, selective participation or masking must be carried out by way of a sequential scan of the memory addresses, which essentially defeats the basic purpose (effectively simultaneous reading of the contents of all memory devices) of the memory.